Lube base oil is a mixture of hydrocarbons having ranging carbon numbers from 15 to 50 that is used as major stock for lubricating oil. The base oil mainly consists of paraffinic compounds containing minor impurities, such as aromatics, naphthenes and olefins. The most important properties of lube base oil are viscosity index and pour point. Viscosity index is an indicator for viscosity stability for the lube base oil. Paraffins—particularly iso-paraffins—have a higher viscosity index than other groups of compounds while keeping pour point in acceptable range. N-paraffins have high viscosity index but high pour point, and thus are solid or very thick liquid under ambient conditions. In some instances, lube base oil may have a viscosity index higher than 120 and a pour point of −24° C. to −12° C.
Lube base oil is conventionally produced from crude oil or other hydrocarbon sources, such as coal liquid. Most lube base oil comes from crude oil distillation. In order to yield a product with the requisite viscosity index, pour point, and oxidative stability, many steps are required. Typical processing units for lube base oil production include solvent extraction, catalytic dewaxing, catalytic hydroprocessing, and combination of these. Solvent extraction generally extracts aromatics from vacuum gas oil for preparing highly paraffinic fractions that are eventually converted to lube base oil after certain operations, including catalytic dewaxing and hydrofinishing. When solvent extraction is the first step to produce lube base oil, the available amount of paraffinic compounds are restricted because of the limited conversion capability of catalytic dewaxing and hydrofinishing. Moreover, solvent extraction is ineffective at removing aromatics and other impurities. Specifically, the presence of a small amount of naphthenes (cycloalkanes) in lube base oil can greatly reduce the viscosity index.
Hydrocracking is also used to produce lube base oil; however, hydrocracking does not significantly increase the amount of paraffinic compounds but rather is limited to the amount of paraffinic compounds present in crude oil. Hydrocracking also consumes a large amount of hydrogen and requires a high severity process to sufficiently crack long paraffinic compounds.
Thermal processing procedures, such as catalytic hydroprocessing and delayed coking, are also conventionally utilized in the production of lube base oil; however, thermal processing detrimentally produces a large amount of low economic value products, such as light gas and solid coke. In delayed coking, where molecules in the petroleum feed may be converted to light gas and solid coke through radical reactions, the product may have light gases and solid coke present in amounts as high as 10 weight % and 30 weight %, respectively.